This invention relates to blood sampling, and more particularly relates to a syringe for collecting a blood gas sample having improved air-sample separation means.
Samples for blood gas analysis have conventionally been collected in syringes having some means to vent air in the syringe prior to sample collection and to protect the sample from external air after collection. Many prior art devices accomplish venting with a filter across a hollow plunger rod which allows passage of air, but not blood, from the interior of the syringe during collection. U.S. Pat. No. 4,821,738 uses a hydrophobic filter and is exemplary of this art. U.S. Pat. No. 4,424,817 uses filters of paper or styrofoam and, in one embodiment, uses two filters, one hydrophilic and one hydrophobic.
U.S. Pat. No. 5,238,003 includes a perforated or slotted disc having upper and lower faces which enclose a hydrophobic filter. The patent adds additional structure which allows the syringe plunger to be advanced during sample collection and thereby overcomes the problem, imposed by conventional fixed plungers, which may cause insufficient sample collection from a patient having low blood pressure.
A porous substrate includes a plastic body portion having a hydrogel coated thereon. In this disclosure the term hydrogel is used to designate a crosslinked polymeric coating on the substrate surface, and the term hydrophilic polymer is used to designate the material which upon crosslinking gives the hydrogel.
The porous substrate may be a component of a medical article. The preferred article is an arterial blood gas syringe having a barrel and a hollow plunger rod wherein the substrate is a plug fitted into the rod. The preferred hydrophilic polymer is polyvinyl pyrrolidone (PVP) and the preferred hydrogel is PVP which has been crosslinked and bound to an inside wall surface of a pore of the plug by electron beam or gamma irradiation.
The plug is permeable to air until the hydrogel coating swells by absorption of water when in contact with blood. The swelling closes the pores to passage of both air and blood and thereby seals the blood sample from the external environment. Because the hydrogel is permanently affixed to the article surface, it cannot be washed away by contact with the blood. The coating is applied without use of any environmentally unfriendly solvents, and the article may be sterilized by radiation used to crosslink the polymer and bind the resulting hydrogel to the substrate.